This invention relates to an ignition coil assembly for an internal combustion engine and, in particular, to such a device mounted directly onto its associated spark plug.
In order to provide enhanced ignition performance, modern internal combustion engines used in automotive applications employ an ignition coil mounted directly on each of the spark plugs. Various styles of directly mounted ignition coils are used in which an ignition coil is mounted to a spark plug or adjacent to an associated spark plug without the need for a long flexible high voltage lead. Variations include so-called xe2x80x9cpencilxe2x80x9d, xe2x80x9cstickxe2x80x9d, xe2x80x9ccigarxe2x80x9d, xe2x80x9cplug holexe2x80x9d or. xe2x80x9ccoil-on-plugxe2x80x9d type ignition coils. Modern ignition systems generate extremely high voltages necessary to precisely and reliably initiate the combustion process within the combustion chamber. Directly mounted ignition coils provide numerous advantages over other types including: elimination of high voltage leads, elimination of xe2x80x9cwaste sparkxe2x80x9d mode, and packaging benefits. Typically, a soft rubber boot is used to encase the spark plug, which is an extension of the coil-on-plug assembly.
The electrical connection between the high voltage terminal of the ignition coil and the spark plug terminal is very important. A reliable and secure connection must be made and it has been found that conventional coil spring type connectors can lead to ignition system failures when the cut end portions of the spring ends cause electromagnetic field concentrations. This can lead to dielectric failure of the ignition coil (i.e., arcing between the spring to a conductive surface outside the rubber boot). The ignition coil assembly is inserted substantially inside the spark plug insertion hole in the cylinder head of the internal combustion engine and, therefore, it is surrounded by an electrical ground. If a point of electro-magnetic field concentration is present at a location where the gap between it and a ground surface is small, dielectric failure can occur.
In addition to the design consideration mentioned previously, the ignition coil assembly must provide a reliable electrical connection, enable servicing, and minimize the number of separate components, and especially loose parts, which tend to lead to assembly related defects.
Other types of ignition coil connectors are also presently used. For example, metal springs or clips can be rigidly attached to the high voltage terminal on the coil-on-plug ignition coil assembly. In order to prevent the spring or clip from falling out of the ignition coil assembly spark plug boot, this design approach requires the spring or clip to be pushed onto and over the high voltage terminal. These configurations are not ideal for certain installation and packaging design approaches.
In accordance with this invention, a directly mounted type ignition coil assembly is provided having a spark plug boot section formed of a highly resilient material. A coil type high voltage connection spring is installed in the boot section and at opposite ends, electrically contacts the coil and spark plug high voltage terminals. Preferably, the end segments of the spring have a smaller bending radius than the spring center section to avoid problems associated with the electro-magnetic field concentrations mentioned previously since the cut ends are positioned to create a large gap to a ground surface. The internal passageway of the coil boot features a generally uniform cylindrical diameter. However, a number of ribs are provided which engage the center section of the spring so that the spring can be retained in the boot before the ignition coil is installed on the spark plug. The ribs are formed in a manner that does not interfere with the molding of the boot section.
The high voltage connection spring is inserted into the orifice of the spark plug boot section and is pressed into position such that it engages the boot passageway ribs. When the coil assembly is installed on the spark plug, the spring is compressed and pushed past the area where the ribs are present. During servicing, when the ignition coil assembly is removed, the spring is allowed to expand, but again engages with the ribs, preventing the spring from falling out of the ignition coil assembly.
The ignition coil assembly in accordance with this invention provides the advantages of a connector which is rigidly connected in that the parts are retained, yet avoids the shortcomings of such designs which can lead to failures mentioned previously.